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outdoor special effects shoot: which diffusion?


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#1 Sherwin Akbarzadeh

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Posted 21 January 2011 - 02:59 AM

Hi,

I've got a special effects shoot involving chroma key suits in a sunny outdoor environment. Test shoots have been positive but to help limit shadows and highlights on the suits I want to use diffusion.

My choices are 250 half diffusion and 216 full diffusion. I know that these diffusions cut light by f2 and f2.6 respectively, but what i'm most concerned with is which will produce a more even light. I'm guessing it's the 216 because it's a heavier diffusion but are there are any other factors i'm not considering.

Cheers,
Sherwin
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#2 David Mullen ASC

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Posted 21 January 2011 - 11:36 AM

Hi,

I've got a special effects shoot involving chroma key suits in a sunny outdoor environment. Test shoots have been positive but to help limit shadows and highlights on the suits I want to use diffusion.

My choices are 250 half diffusion and 216 full diffusion. I know that these diffusions cut light by f2 and f2.6 respectively, but what i'm most concerned with is which will produce a more even light. I'm guessing it's the 216 because it's a heavier diffusion but are there are any other factors i'm not considering.

Cheers,
Sherwin


Do you mean overhead diffusion to soften the sun? You'd have to go very big to cover a standing person head to toe plus not see the shadow of the frame right around their feet, at least 20'x20', which takes a crew of a certain size to handle and secure.

If so, generally you don't have the option of plastic diffusion like 216, though there are some Frost diffusions that are like shower curtain material. A Full Silk is probably want you'd want.

If you are talking about a frame of diffusion in front of a light, yes, 216 is softer than 250, the other factor is that the light should fill the frame evenly because the softness is determined by the size of the source relative to the distance to the subject, and when using diffusion, the frame becomes the source, not the light behind it. So a 6'x6' is softer than a 4'x4', for example, if the same distance to the subject and if the frame is filled evenly.

You can always double-diffuse, for example, put a 250 intermediate frame between the light and the 216 frame.

If you are talking about 250 and 216, it sounds like you are thinking of 4'x4' frames and smaller, which isn't particularly soft unless very close to the actors in a medium to close shot. Generally the old rule for soft portrait lighting is that the size of the diffusion should be the size of the subject in the frame, so head-to-toe shots would require a 6'x6' frame of diffusion, etc. If you want a very soft source.
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#3 Sherwin Akbarzadeh

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Posted 23 January 2011 - 01:41 AM

Thanks for taking the time David, I was indeed talking about 4' x 4' frames. Sorry not to make that clear initially. I'm aware that this limits me to use diffusion only on medium shots and close ups. Shame I don't have a bigger crew for a 20' x 20' frame. I've just got one guy on a stepladder! So you can imagine the kind of distance he'll be from the subject if he's trying to block the sun near the middle of the day - around 2-3 metres tops.

To produce the most even light i'm going to go with the full silk 216. The important thing is that I'm softening the light so that I can key out the subject effectively. So even if I have to underexpose the subject a little bit to get the right exposure on the background, it won't matter.

Sherwin
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#4 David Mullen ASC

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Posted 23 January 2011 - 01:52 AM

T
To produce the most even light i'm going to go with the full silk 216.


"Full Silk" and "216" are two different things -- silk is a fabric and 216 is a plastic material.
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#5 Brian Dzyak

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Posted 23 January 2011 - 10:15 AM

...and you really mean to say "Visual Effects," not "Special Effects." Two different things. :)
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#6 Jim Menkol

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Posted 24 January 2011 - 01:18 PM

Recently I used a 12x12 with the shower curtain--it took two people to handle the frame on four combo stands; all the gear cost $160 to rent. We were able to cover a good amount of ground with it, but some correction in post to correct the background, which we were planning on from the start. IMHO shower curtains give some of the best soft light, especially from a large frame.
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#7 Logan Thomas Triplett

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Posted 24 January 2011 - 03:50 PM

Recently I used a 12x12 with the shower curtain--it took two people to handle the frame on four combo stands; all the gear cost $160 to rent. We were able to cover a good amount of ground with it, but some correction in post to correct the background, which we were planning on from the start. IMHO shower curtains give some of the best soft light, especially from a large frame.



I was the DP on the shoot Jim was referring to, it worked great under our circumstances. We did have to fight the sun, and at the highest point of the sun we were forced to move in to close-ups, on the budget we had, the 12' covered the area that we needed fairly well. Once again we didn't have a 20x available, but for the cost, the 12x shower curtain did the job! I loved the shower curtain! With a sunny background, it made the subjects appear to be still in sunlight, unlike a silk which just diffuses too much light for what we were trying to do. I also took smaller silks on C-stands and had the crew break up the shower curtain a bit to give it a little less consistency, and was very pleased with the results!

Here are a few screen captures:
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I'm not sure what type of area you are attempting to diffuse though! And i havent had a lot of experience with keying outside via the sun

Good Luck!
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